EP0468893B1 - Process for the manufacture of a reinforced plastic component, and use thereof as support for ripening cheese - Google Patents

Description

The invention relates first of all to a method of manufacturing by molding, in a mold cavity, a part comprising a plastic wall connected to a layer also made of plastic which coats a mechanically resistant reinforcement. The invention also relates to the part itself.

Practically all manufacturers of plastic parts, for example polypropylene, are today confronted with problems of cracks or twisting of the parts when they are reinforced with a frame (generally metallic), the natural shrinkage of the plastic creating delicate contraction forces to control and often damaging for the parts see for example FR-A-957 422.

The object of the invention is to provide a solution to these problems, in particular in the case where the parts are in the form of a tray having a central wall of plastic material with a peripheral metal frame coated with plastic material.

• a) on place l'armature de raidissement dans le moule, on remplit l'empreinte du moule avec de la matière plastique fluide reliant, par au moins un pont, la matière des cavités de moule correspondant à la paroi de la pièce et à ladite couche d'enrobage, respectivement, le pont étant conformé avant rétraction de la matière plastique pour y ménager une réserve de longueur formant une marge prédéterminée de déformation utilisable lors du retrait,
• b) et ensuite, on ouvre le moule et démoule la pièce avant la fin du retrait intervenant lors de la solidification de la matière plastique pour laisser les ponts de déformer en suivant la rétraction de cette matière.

To this end, the molding process which is the subject of the invention is characterized in particular in that in which process:

• a) the stiffening frame is placed in the mold, the mold cavity is filled with fluid plastic material connecting, by at least one bridge, the material of the mold cavities corresponding to the wall of the part and to said coating layer, respectively, the bridge being shaped before shrinkage of the plastic to provide a length reserve forming a predetermined margin of deformation usable during removal,
• b) and then, the mold is opened and the part is demolded before the end of the withdrawal occurring during the solidification of the plastic material to leave the deform bridges following the retraction of this material.

Thus, we can control the shrinkage of the plastic during its solidification by concentrating a significant part of the contraction forces to the location of the connecting bridge (s) in question, the deformation, with for example articulation in rotation of the latter, greatly limiting the problems of twisting as well as the appearance of cracks.

Preferably, according to another characteristic of the invention, the said wall being produced to be substantially planar, it will advantageously be adjusted from the outset, before the plastic material shrinks, the deformation margin of the bridge (s) for keep its flatness on the wall after removal.

As for the part in itself finally obtained in accordance with the invention, different embodiments can be envisaged.

In a first variant, the part may be in the general form of a tray comprising in the central part a substantially flat wall of plastic material connected peripherally, by several of said aforementioned bridges, to a layer of plastic material coating a frame forming a frame around said wall, the bridges which form a single piece with the material of this wall and of said layer having at least one groove formed at the junction between said wall and these bridges and / or between the latter and said coating layer.

In another variant of this same part, each material bridge may be inclined angularly (substantially in the same plane as the central wall) relative to one of the radiating directions passing through the center of the wall and intersecting the bridge considered.

According to a third variant, which could be associated with the second, said connecting bridges could have a sinuous shape, this always substantially in the plane of the central wall.

Finally, the invention relates to the use of such an armed piece with controlled withdrawal to obtain a support plate for heavy cheese, during maturation, such as emmenthal.

• la figure 1 montre une vue de face d'une pièce présentant les caractéristiques de l'invention,
• la figure 2 est une demi-coupe agrandie de la pièce de la figure 1 dans le sens de la ligne II-II de cette même figure 1,
• les figures 3 et 4 illustrent également, en demi-vue de coupe identiques à celle de la figure 2, deux étapes successives de réalisation de la pièce de la figure 1,
• la figure 5 est une vue schématique d'ensemble d'une variante de réalisation de la pièce de la figure 1,
• la figure 6 est une vue agrandie d'un détail de réalisation du plateau de la figure 5,
• la figure 7 est une vue en coupe selon la ligne VII-VII de la figure 6,
• et les figures 8 et 9 montrent la configuration de quelques languettes de liaison au moment du moulage alors que la matière plastique est encore fluide (figure 8) et après solidification et retrait de cette même matière (figure 9).

The invention, its characteristics and advantages will appear more clearly from the description which follows, given with reference to the accompanying drawings given solely by way of nonlimiting examples and in which:

• FIG. 1 shows a front view of a part having the characteristics of the invention,
• FIG. 2 is an enlarged half-section of the part of FIG. 1 in the direction of line II-II of this same FIG. 1,
• FIGS. 3 and 4 also illustrate, in half-sectional view identical to that of FIG. 2, two successive stages in the production of the part in FIG. 1,
• FIG. 5 is a schematic overall view of an alternative embodiment of the part of FIG. 1,
• FIG. 6 is an enlarged view of an embodiment detail of the tray of FIG. 5,
• FIG. 7 is a sectional view along line VII-VII of FIG. 6,
• and Figures 8 and 9 show the configuration of some connecting tabs at the time of molding while the plastic is still fluid (Figure 8) and after solidification and removal of the same material (Figure 9).

Firstly, in FIGS. 1 and 2, a tray is shown, for example intended to receive a relatively heavy and bulky cheese on it, such as Emmenthal during maturation.

The plate 1 comprises a substantially flat central wall 2 made of plastic material (such as polypropylene for example), surrounded in this case over its entire periphery by a reinforcement or stiffening frame 4, such as a metal frame with a substantially circular section .

For its protection and its connection with the wall 2, the frame 4 is coated with a layer 6 of the same plastic material as that of the wall 2 and is connected to the latter, in one piece, by a series of bridges of material 8. Each bridge is separated from the next by an opening 9.

In FIG. 1, it will be noted that taking into account the shape of a circular plate of the part 1, all the bridges 8 are identical and substantially regularly distributed radially around the periphery of the wall 2 in the general plane 3 of which they are extend, part 1 having been shown in the figures in its "ready to use" state, that is to say after removal of the plastic.

In FIG. 2, the substantially common axis of the part 2 and of a bridge 8 has been identified.

In the figures, it also appears clearly that in a radial direction, the radial length l of the bridges is very much less than the radius R of the central wall 2. By way of example, one can in particular envisage a ratio of the order from 1 to 20.

At its radial ends, each bridge has thinner transverse grooves 12, 14. These grooves 12, 14 have in particular the role of serving as privileged areas of articulation in rotation of the bridges, during the withdrawal, this in a succession of radial planes substantially perpendicular to that of the wall 2, thus allowing relative movement in length of this wall and of the frame 4.

By thus concentrating a large part of the natural forces of contraction of the material at the location of the bridges 8 which will deform in a controlled or directed manner under the tension of this material, it will be possible to absorb, according to the tests carried out, between 40 and About 70% of the shrinkage, this in a regular and balanced way around the perimeter of the room.

In FIG. 2 in particular, it will be noted that provision may be made, to further stiffen the part externally, to extend the coating layer 6 on the side opposite to the bridges 8, by a peripheral axial rib 16 which may be surrounded by a transverse rib 18.

Since the tray illustrated in the figures is in particular intended to be used as a cheese support tray, it has been considered preferable to provide in the wall 2, from place to place, air circulation means 20 formed hollow in this wall.

As can be seen more clearly in FIG. 2, these ventilation means may consist of orifices passing through the wall 2.

The distribution of these orifices will depend on the desired level of ventilation, the aspect relating to the mechanical strength of the wall must of course also be taken into consideration.

Optionally, other means of air circulation could be envisaged, such as for example grooves or grooves.

From Figures 3 and 4, we will now briefly present a manufacturing process that can be implemented to achieve the type of part which has just been described.

Firstly, in FIG. 3, it can be seen that the plate 1 has been shown as it is inside the mold used for its manufacture (not shown) when the mold is to be poured or injected. plastic material, after having of course taken care to correctly place the stiffening frame 4 in the mold.

In this first manufacturing phase, we will thus fill plastic material (liquid or flexible at its processing temperature) the mold cavity then closed to make in one piece, the wall 2, the coating layer 6 of the frame and its short internal extension connecting it to the series of connections 8 with their groove (s) 12, 14.

To reserve at the location of these connections 8 a margin of deformation which can be used during removal, here we have chosen to produce the bands 8 giving them original, while the plastic is still fluid in the mold, an angle d 'inclination α relative to the general surface of the wall 2, thus shifting the latter relative to its peripheral frame (see Figure 3).

The mold is then of course closed.

On the other hand, as soon as this operation is finished and above all before the plastic material solidifies by contracting, we will open the mold and preferably unmold the part to allow the connections 8 to deform freely.

There is then gradually an alignment of the wall 2 and of its reinforcement (see FIG. 4), the initial angle α tending to decrease as the shrinkage takes place.

As can be clearly seen in FIG. 4, it will thus be possible to obtain, at the end of withdrawal, a substantially flat part under reasonable tension, the original angle of inclination having practically disappeared.

It will be understood that this initial angle will vary in particular depending on the plastic material used and the size of the part to be manufactured. An angle between 30 and 60 ° should be suitable.

In practice, it is advisable to adjust this original angle, to obtain, after removal, a compromise between the flatness under load of the wall of the plate and the tension force then exerted essentially on the frame.

In FIGS. 3 and 4, it will be noted that, unlike FIGS. 1 and 2 where the zones of thinner thickness 12, 14 have been formed by a substantially symmetrical narrowing of material on the two opposite faces of the part, the hinges 12 ′ And 14 ′ of each tab were produced respectively on one side and on the other of the part, depending on the direction of rotation adopted.

More specifically, in this example, the first hinge 12 ′ between the wall 2 and the considered connection strip was formed on the side of the “upper” face 22 of the part, the second opposite hinge 14 ′ having here been formed on the "lower" face 32. For the sake of clarity, the terms SUP and INF have indicated the sides chosen arbitrarily in FIG. 3 as upper and lower.

Of course, all the intermediate solutions could be envisaged, such as for example those providing a single hinge or a double hinge formed on the same face at the two ends of each tongue 8.

It should also be quite clear that numerous alternative embodiments of a part in accordance with the invention could be imagined. In particular, we could provide to connect the wall 2 and the layer 6 connected to the coating of the frame by a strip forming a continuous bridge of material, which can if necessary have a thickness less than that of the wall 2. One could also imagine making rectangular trays or any other shape.

The invention could also be applied to the production of a wall which would be connected only on one of its side edges to a coated stiffening reinforcement, this by a deformable strip which would be either continuous or discontinuous with openings d 'spacing.

In FIGS. 5 to 9, an alternative embodiment of the invention has also been illustrated, in which there is notably (see FIG. 5) a plate 40 with a substantially flat central panel 42 of plastic material surrounded peripherally by a frame 44 , which is coated with a layer 46 of the same plastic as that of the panel, thin tabs 48 separated by interstices 49 ensuring the connection extending substantially in the plane 43 of the panel.

To ensure the reserve or margin of length which can be used during removal, the tongues 48 may have an original sinuosity, for example in "S" shape formed in the plane 43.

For the same purpose, each tongue, which here has an elongated shape substantially in a bar, can be oriented in the direction of its length with an angular inclination β (Figure 2) relative to the corresponding radiating direction 41 passing through the center 45 of the tray (Figure 5).

In practice, a sinuous shape may be preferred to a rectilinear bias shape in so far as it allows radial end connections of tongues 48a, 48b extending in the direction of the corresponding radiating axes.

Regarding the ventilation openings 50 of the panel 42, it will be noted that in this case, they are in a rectangular shape, giving the tray the appearance of a trellis whose outermost branches are peripherally, identified 55 in FIG. 6, may come directly in the extension of the opposite connection ends 48b of the tongues 48.

With regard to the method of manufacturing this plate 40, it will simply be noted that the original, during the molding of the part and while the plastic is still flexible, that is to say before removal, it will conform to inside the mold, the tongues 48 in the general plane of the plate with advantageously a fairly pronounced angular offset β (for example of the order of 15 to 25 °) so as to have over the entire peripheral zone of the panel, a deformation zone having this reserve of length or deformation margin which will be able to be absorbed during the removal in particular of the panel 42, at the moment when the plastic material will solidify.

Of course, at this moment, the tongues 8 will then have to be able to deform freely and thus pass from their shape in FIG. 8 to that of FIG. 9 where there is a less marked sinuosity corresponding to a contraction of the wall 42 in particular.

In practice, the number, the length and the angular orientation β of the tongues will be adapted to ensure a compromise between the flatness under load of the panel and the tension forces exerted in particular on the frame.

Claims (11)

1. Method of moulding, in a mould hollow, a piece comprising a wall (2, 42) of plastics material connected to a plastics material covering (6, 46), encasing a reinforcement member (4, 44), in which method:

   a) the stiffening reinforcement member is placed in the mould, the hollow of the mould is filled with plastics material fluid connecting, by at least one bridge, (8, 48), the material of the cavities of the mould corresponding to the wall of the piece and to said encasing covering respectively, the bridge being formed before the plastics material is shrunk so as to provide it with a reserve of length forming a predetermined deformation margin which can be used during the shrinkage;

   b) and, subsequently, the mould is opened and the piece is ejected before the end of the shrinking occurring during the setting of the plastics material, to allow the bridges to deform according to the shrinkage of this material.
2. Method according to Claim 1,
   characterised in that:

   - during stage a), the connecting bridge(s) (8) are produced so that it has/they have, before the plastics material shrinks, an inclination (α) in relation to said wall (2) of the piece and comprise(s) at least one articulation hinge (12, 14, 12', 14') which pivots in relation to this wall (2) and/or in relation to the covering (6) encasing the reinforcement;

   - then, in stage b), the material is allowed to contract, so that this shrinkage causes a reduction in the angle of inclination of the bridge(s) in relation to said wall (2), with a pivoting at the location of the hinge(s).
3. Process according to Claim 1,
   characterised in that:

   - during stage a), said wall (42) of the piece is produced in a substantially flat manner and the connection bridge(s) are formed in this plane; and

   - then, during stage b), said bridge(s) (48) are allowed to deform in the general plane (43) of the wall.
4. Method according to Claim 3,
   characterised in that during stage a), the bridge(s) (48) is/are formed such that it has/they have a marked winding.
5. Method according to Claim 1,
   characterised in that, said wall (2, 42) being produced so as to be substantially flat, the deformation margin of the bridge(s) (8, 48) is adjusted at the start, before the plastic material shrinks, so that the flatness of said wall is retained after shrinking.
6. Piece obtained by performing the method according to any one of Claims 1, 2 or 5, characterised in that it is in the general shape of a plate, comprising, in the central part, a plastics material wall (2) which is substantially flat, connected at the periphery by bridges of the material (8) to a plastics material covering (6) which encases a reinforcement member (4) forming a frame about said wall (2), said bridges (8), which form a single piece with the material of this wall, and said covering (6) having at least one throat (12, 14; 12', 14') provided at the point of the connection between said wall (2) and said bridges and/or between these latter and said surrounding coverings (6).
7. Piece according to Claim 6, characterised in that it has two opposite faces (22, 32) as well as two said throats (12, 14; 12', 14') for each bridge, the throats opening on both faces of the piece.
8. Piece obtained by performing the method according to any one of Claims 1 or 3 to 5, characterised in that it is in the general form of a plate comprising, in the central part, a wall (42) which is substantially of plastics material, connected at the periphery by bridges of the material (48) to a covering (46) of plastics material which encases a reinforcement member (44) forming a frame about said wall (42), each bridge, which forms a single piece with the material of said wall (42) and said layer (46), being directed in the general plane (43) of the wall (42) with an angular inclination (β) in relation to one of the radial directions passing through the centre of this wall and crossing the corresponding bridge.
9. Piece obtained by performing the process according to any one of Claims 1 or 3 to 5, characterised in that it is in the general shape of a plate comprising, in the central part, a substantially flat wall (42) of plastics material connected at the periphery by bridges of the material (48) to a plastics material covering (46) which encases a reinforcement member (44) forming a frame about said wall (42), said bridges (48), which form a single piece with the material of the wall (42) and of said layer (46), having a winding shape substantially in the general plane (43) of this wall.
10. Piece according to any one of Claims 6 to 9, characterised in that said bridges consist of tongues separated by apertures (9, 49) and distributed substantially regularly one after another on the circumference of the central wall (2, 42).
11. Application of the piece according to any one of Claims 6 to 10 as a supporting plate for cheese, such as emmantal, while it is maturing.

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